OK what are MOD's, i see alot of people talking about them and i kinda got that their visual upgrades to the game for extra scenery or somthing holidays whatnot, but once you put one in, doesnt it erase your original files and how do you take them out, i have seen a couple from the last game *vv1* in screen shots and on the examples, but i dont want to permanetly erase the original theme. just a good explaination on how to do it would be wonderfull thanks